Feedback method and apparatus for cooperative communication system

ABSTRACT

Methods and apparatuses are provided for transmitting channel information, by a User Equipment (UE). Information for at least one first type Channel Status Information Reference Signal (CSI-RS) and information for at least one second type CSI-RS from an eNB, are identified. First channel information is generated based on a first set of a first type CSI-RS and a second type CSI-RS. Second channel information is generated based on a second set of a first type CSI-RS and a second type CSI-RS. The first channel information is reported by Physical Uplink Control CHannel (PUCCH)-based periodic channel information feedback. The second channel information is reported by the PUCCH-based periodic channel information feedback.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 14/309,456, which was filed in the U.S. Patent andTrademark Office (USPTO) on Jun. 19, 2014, which is a ContinuationApplication of U.S. patent application Ser. No. 13/525,958, which wasfiled in the USPTO on Jun. 18, 2012, now U.S. Pat. No. 9,125,189, issuedon Sep. 1, 2015, which claims priority under 35 U.S.C. §119(a) to KoreanPatent Application No. 10-2011-0059289, which was filed in the KoreanIntellectual Property Office on Jun. 17, 2011, the disclosures of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method and apparatus forgenerating feedback signal in a cellular mobile communication systemincluding a plurality of base stations and, more particularly, to afeedback method and apparatus for Cooperative Multi-Point (CoMP) inwhich multiple base stations cooperate with each other for downlinktransmission to a terminal.

2. Description of the Related Art

Mobile communication systems have evolved into high-speed, high-qualitywireless packet data communication systems to provide data andmultimedia services beyond the early voice-oriented services. Recently,various mobile communication standards, such as High Speed DownlinkPacket Access (HSDPA), High Speed

Uplink Packet Access (HSUPA), Long Term Evolution (LTE), andLTE-Advanced (LTE-A) defined in 3^(rd) Generation Partnership Project(3GPP), High Rate Packet Data (HRPD) defined in ^(3rd) GenerationPartnership Project-2 (3GPP2), and 802.16 defined in IEEE, have beendeveloped to support high-speed, high-quality wireless packet datacommunication services.

Particularly, the LTE-A communication standard has been developed tosupport high speed packet data transmission and to maximize thethroughput of the radio communication system with various radio accesstechnologies. LTE-A is the evolved version of LTE to improve datatransmission capability.

The existing 3^(rd) generation wireless packet data communicationsystems (including HSDPA, HSUPA and HRPD) adopt Adaptive Modulation andCoding (AMC) and Channel-Sensitive Scheduling techniques to improvetransmission efficiency.

In the wireless packet data communication system adopting AMC, thetransmitter is capable of adjusting the data transmission amount basedon channel conditions. That is, the transmitter decreases the datatransmission amount for bad channel conditions so as to fix the receivedsignal error probability at a certain level and increases the datatransmission amount for good channel conditions so as to efficientlytransmit a large amount of information while maintaining the receivedsignal error probability at an intended level.

In the wireless packet data communication system adopting channelsensitive scheduling, the transmitter serves the user having a goodchannel condition first among a plurality of users so as to increase thesystem capacity as compared to allocating a channel to just one user.Such increase of system capacity is referred to as multi-user diversitygain.

When using AMC along with a Multiple Input Multiple Output (MIMO)transmission scheme, it may be necessary to take into consideration thenumber of spatial layers and ranks for transmitting signals. In thiscase, the transmitter determines the optimal data rate in considerationof the number of layers for use in MIMO transmission.

In general, OFDMA is expected to provide superior system throughput ascompared to CDMA. One of the main factors that allows OFDMA to increasesystem throughput is the frequency domain scheduling capability. Aschannel sensitive scheduling increases system capacity usingtime-varying channel characteristics, OFDMA can be used to obtain morecapacity gain using frequency-varying channel characteristics. Recently,research is being conducted to replace Code Division Multiple Access(CDMA) used in the legacy 2^(nd) and 3^(rd) mobile communication systemswith Orthogonal Frequency Division Multiple Access (OFDMA) for the nextgeneration mobile communication system. 3GPP and 3GPP2 are in the middleof the standardization of an OFDMA-based evolved system.

FIG. 1 is a diagram illustrating a conventional cellular mobilecommunication system in which the transmit/receive antenna is arrangedat the center of the cells.

Referring to FIG. 1, in the cellular mobile communication systemincluding a plurality of cells, a User Equipment (UE) receives mobilecommunication service from a cell selected for a semi-static durationwith the above described techniques. Suppose that the cellular mobilecommunication system includes three cells 100, 110, and 120. Also,suppose the cell 100 serves the UEs 101 and 102 within its service area,the cell 110 serves the UE 111, and the cell 120 serves the UE 121.

The UE 102 served by the cell 100 is located far from the antenna 130 ascompared to the UE 101. In this case, the UE 102 experiences significantinterference from the central antenna of the neighbor cell 120 so as tobe served by the UE 100 at a relatively low data rate.

When the cells 100, 110, and 120 provide the mobile communicationservice independently, they transmit Reference Signals (RSs) fordownlink channel estimation at the recipient. Particularly in the 3GPPLTE-A system, the UE measures the channel condition between the eNB anditself using a Channel Status Information Reference Signal (CSI-RS)transmitted by the eNB.

FIG. 2 is a diagram illustrating a resource block including an CSI-RStransmitted from an eNB to a UE in a conventional LTE-A system.

Referring to FIG. 2, two CSI-RS antenna port signals are mapped to eachof the positions 200 to 219. That is, the eNB transmits two CSI-RSs fordownlink measurement to the UE at the position 200. When the cellularmobile communication system includes a plurality of cells as depicted inFIG. 1, the CSI-RS is transmitted in different positions correspondingto the respective cells. For example, the CSI-RS is transmitted at theposition 200 for the cell 100, the position 205 for the cell 110, andthe position 210 for the cell 120. The reason why the cells areallocated resources at different positions for CSI-RS transmission is toprevent the CSI-RSs of different cells from interfering among eachother.

The permutation of CSI-RSs transmitted at the positions of the CSI-RSantenna ports are defined by Equation (1).

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots \mspace{14mu},{N_{RB}^{\max,{DL}} - 1}} & (1)\end{matrix}$

In Equation (1), c denotes the pseudo-random permutation, and theinitial value of the permutation generator is defined by Equation (2).

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID) ^(cell)+N _(CP)   (2)

In Equation (2), l denotes an OFDM symbol order in a slot, and N_(CP)denotes the length of a cyclic prefix (CP) used in the cell and is setto 0 or 1.

In the cellular mobile communication system depicted in FIG. 1, the UElocated at the cell edge is limited in data rate due to significantinterference from neighbor cells. This means that the data rate of theUE is influenced significantly by its location within the cell in thecellular mobile communication system depicted in FIG. 1. That is,although the conventional cellular mobile communication system may servethe UE located near the center of the cell at a high data rate, it isimpossible to serve the UE located far from the center of the cell at ahigher data rate.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve theabove-described problems and it is an aspect of the present invention toprovide a feedback method and apparatus that is capable of facilitatingCoMP transmission in an LTE-A system.

In accordance with an aspect of the present invention, a method isprovided for transmitting channel information, by a UE. Information forat least one first type CSI-RS and information for at least one secondtype CSI-RS from an eNB, are identified. First channel information isgenerated based on a first set of a first type CSI-RS and a second typeCSI-RS. Second channel information is generated based on a second set ofa first type CSI-RS and a second type CSI-RS. The first channelinformation is reported by Physical Uplink Control CHannel (PUCCH)-basedperiodic channel information feedback. The second channel information isreported by the PUCCH-based periodic channel information feedback.

In accordance with another aspect of the present invention, a method isprovided for receiving channel information, by a eNB. Information for atleast one first type CSI-RS and information for at least one second typeCSI-RS is transmitted to a UE. First channel information is received byPUCCH-based periodic channel information feedback. Second channelinformation is received by the PUCCH-based periodic channel informationfeedback. The first channel information is generated based on a firstset of a first type CSI-RS and a second type CSI-RS. The second channelinformation is generated based on a second set of a first type CSI-RSand a second type CSI-RS.

In accordance with another aspect of the present invention, a userequipment is provided for transmitting channel information. The userequipment includes a communication unit configured to transmit andreceive signals. The user equipment also includes a control unitconfigured to control identifying information for at least one firsttype CSI-RS and information for at least one second type CSI-RS from aneNB. The control unit is also configured to control generating firstchannel information based on a first set of a first type CSI-RS and asecond type CSI-RS. The control unit is also configured to controlgenerating second channel information based on a second set of a firsttype CSI-RS and a second type CSI-RS. The control unit is alsoconfigured to control reporting the first channel information byPUCCH-based periodic channel information feedback. The control unit isalso configured to control reporting the second channel information bythe PUCCH-based periodic channel information feedback.

In accordance with still another aspect of the present invention, an eNBis provided for receiving channel information. The eNB includes acommunication unit configured to transmit and receive signals. The eNBalso includes a control unit configured to control transmittinginformation for at least one first type CSI-RS and information for atleast one second type CSI-RS to a UE. The control unit is alsoconfigured to control receiving first channel information by PUCCH-basedperiodic channel information feedback. The control unit is alsoconfigured to control receiving second channel information by thePUCCH-based periodic channel information feedback. The first channelinformation is generated based on a first set of a first type CSI-RS anda second type CSI-RS. The second channel information is generated basedon a second set of a first type CSI-RS and a second type CSI-RS.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a conventional cellular mobilecommunication system in which a transmit/receive antenna is arranged ata center of cells;

FIG. 2 is a diagram illustrating a resource block including a CSI-RStransmitted from an eNB to a UE in a conventional LTE-A system;

FIG. 3 is a diagram illustrating a cellular mobile communication systemaccording to an embodiment of the present invention;

FIG. 4 is a diagram illustrating a resource block including a CSI-RStransmitted from an eNB to a UE according to an embodiment of thepresent invention; FIG. 5 is a flowchart illustrating a UE procedure forfeedback in a DS-based cellular mobile communication system according toan embodiment of the present invention;

FIG. 6 is a flowchart illustrating a UE procedure for feedback in aDB-based cellular mobile communication system according to an embodimentof the present invention;

FIG. 7 is a flowchart illustrating a feedback method in a DB-basedcellular mobile communication system adapted to the type of the UEaccording to an embodiment of the present invention;

FIG. 8 is a schematic block diagram illustrating a UE according to anembodiment of the present invention; and

FIG. 9 is a schematic block diagram illustrating a central controlleraccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention are described withreference to the accompanying drawings in detail. Detailed descriptionof well-known functions and structures incorporated herein may beomitted to avoid obscuring the subject matter of the present invention.

Although a detailed description of the present invention is given hereinwith reference to the OFDM-based radio communication system,particularly 3GPP E-UTRA standard system, it will be understood by thoseskilled in the art that the present invention can be applied to othercommunication systems having a similar technical background and channelformat, with a slight modification, without departing from the spiritand scope of the present invention.

The cellular mobile communication system is composed of a plurality ofcells deployed within a restricted area. A cell is defined as ageographic area where UEs are served by an eNB apparatus. A UE is servedby a cell, which is selected semi-statically. Such a system is referredto as a non-CoMP system hereinafter. In the non-CoMP system, the UE isassigned a data rate that varies significantly according to its locationwithin the cell. A UE located near the center of the cell is assigned ahigh data rate while a UE located far from the center of the cell isassigned a low data rate.

A CoMP system is the opposite of the non-CoMP one. The CoMP system is asystem in which multiple cells cooperate for data transmission to the UElocated at the cell edge. The CoMP system is superior to the non-CoMPsystem in quality of mobile communication service. The present inventionprovides a feedback method and apparatus operating based on Dynamic cellSelection (DS) and Dynamic cell Blanking (DB) techniques that arecharacterized by relatively simple operation and improved performance.DS is a method for the UE to measure the channel condition per cell andselect a cell having an optimized channel. DB is a method for one ormore cells that are potentially producing interference to mute datatransmission for predetermined time duration. The present inventionmodifies the feedback structure so as to apply the DS or DB technique tothe LTE-A system to solve the aforementioned problems.

FIG. 3 is a diagram illustrating a cellular mobile communication systemaccording to an embodiment of the present invention. Specifically, FIG.3 is directed to cellular mobile communication systems composed of threecells. In an embodiment of the present invention, the term “cell” meansa service area centered around a specific transmission point, which maybe a Remote Radio Head (RRH) sharing the cell ID with the macro eNBwithin the macro cell or a macro or pico cell having a unique cell ID.

A central controller is an apparatus that is capable of communicatingdata with UEs and processing the data. When the transmission point isthe RRH sharing a cell

ID with the macro eNB, the macro eNB can be referred to as the centralcontroller. When the transmission point is the macro or pico cell havinga unique cell ID, an apparatus managing the cells integrally can bereferred to as the central controller.

Referring to FIG. 3, the cellular mobile communication system includesat least one cell 300, 310 and 320; UEs 301, 311, and 321 which receivedata from the nearest cell; and a UE 302 that receives data in CoMPtransmission from the cells 300, 310, and 320. The UEs which receivedata from the nearest cell 301, 311, and 321 perform channel estimationbased on the Channel Status Information Reference Signal (CSI-RS) forthe cell in which the UEs are located and transmit the correspondingfeedback to the central controller 330. However, the UE 302 which isserved in CoMP transmission from the cells 300, 310, and 320 has toperform channel estimation for each of the three cells. In order for theUE 302 to perform channel estimation, the central controller 330 assignsthree CSI-RSs corresponding to the cells participating in the CoMPtransmission for the UE 302. A description is made of the CSI-RSallocation method with reference to FIG. 4.

FIG. 4 is a diagram illustrating a resource block including a CSI-RStransmitted from an eNB to a UE in the system according to an embodimentof the present invention.

Referring to FIG. 4, the central controller allocates resources 401,402, and 403 for three CSI-RSs such that the UE receiving CoMPtransmission is capable of estimating channels from the cells 300, 310,and 320. The resources are allocated to correspond to the CSI-RSs forchannel estimations in the respective cells. Reference number 401denotes the resource allocated to CSI-RS for channel estimation in thecell 300, reference number 402 denotes the resource allocated to CSI-RSfor channel estimation in the cell 402, and reference number 403 denotesthe resource allocated to CSI-RS for channel estimation in the cell 403.A set of cells having the resource allocated to at least one CSI-RStransmitted for channel estimation of the CoMP UE is referred to as ameasurement set. Although the description is directed to where thecentral controller knows the cell IDs of all cells participating in theCoMP transmission, the present invention is not limited thereto. Thatis, the cells participating in the CoMP transmission share informationon the cell IDs and positions of the resource allocated to therespective cells for cooperative transmission to a UE.

FIG. 5 is a flowchart illustrating a UE procedure for feedback in aDS-based cellular mobile communication system according to an embodimentof the present invention. DS is a technique in which the UE measures thechannel status and selects the cell having the best channel.

Referring to FIG. 5, the UE operating in the DS mode determines at step501 whether it is a CoMP UE. The CoMP UE can be determined based on thefeedback mode requested by the central controller. That is, the centralcontroller notifies the UE of the feedback mode in which the UE is tooperate, in advance. The UE checks the feedback mode to determinewhether it is a CoMP UE.

If it is determined that the UE is a CoMP UE, the UE estimates thechannels of the cells participating in the CoMP transmission based onthe CSI-RSs in the measurement set at step 502. Referring to FIGS. 3 and4, the UE 302 estimates the channels of the cells 300, 310, and 320based on the CSI-RSs 401, 402, and 403 respectively in the measurementset having the resources allocated by the central controller.

Afterward, the UE calculates signal-to-noise plus interference ratio(SINR) for the respective cells and selects a best cell in considerationof additional cell conditions at step 503. Here, the additional cellconditions may be a number of other UEs within a specific cell. Since itis impossible for the UE to check the number of other UEs directly, thecentral controller transmits cell status information including an offsetvalue to the UE. The offset value can be expressed as SINR or aModulation and Coding Scheme (MCS) value. In the case of using theoffset value as SINR or MCS value, the best cell is selected asexpressed by Equations (3) or (4).

i*=arg max_(i) └SINR(R _(i), Σ_(j∈M\(i)) R _(j))+offset_(i)^(SINR)┘  (3)

i*=arg max_(i) └SINR(R _(i), Σ_(j∈M\(i)) R _(j))+ƒ(offset_(i)^(MCS))┘  (4)

In Equations (3) and (4), SINR(A, B) denotes an SINR calculationfunction with input of a receive channel A for signal and anotherreceive channel B for interference. The receive channel A is expressedas R_(i) which denotes the receive channel of the signal transmitted byan i^(th) cell. The receive channel B for interference is expressed asΣ_(j∈M\(i))R_(j), and M denotes the measurement set. In Equation (4), ƒdenotes a function of the UE receiver for converting the MCS value tothe SINR value. In case of setting the offset value as MCS, thecharacteristic of the UE receiver is reflected in the cell selectionprocess so as to give an advantage as compared to the setting the offsetvalue as SINR. Once the best cell has been selected at step 503, the UEfeeds back the cell index of the selected cell and the related channelinformation to the central controller at a predetermined feedback periodat step 504.

Returning to step 501, if it is determined that the UE is not a CoMP UE,the UE performs a non-CoMP operation at step 511. In the non-CoMPoperation, the UE performs channel estimation for the cell transmittingdata thereto and feeds back the channel status information to thecentral controller.

FIG. 6 is a flowchart illustrating a UE procedure for feedback in aDB-based cellular mobile communication system according to an embodimentof the present invention.

Referring to FIG. 6, the UE operating in the DB mode determines at step601 whether it is a CoMP UE. The CoMP UE can be identified based on thefeedback mode requested by the central controller. That is, the centralcontroller notifies the UE of the feedback mode in which the UE is tooperate, in advance. The UE checks the feedback mode to determinewhether it is a CoMP UE.

If it is determined that the UE is a CoMP UE, the UE estimates channelsof the cells participating in the CoMP transmission based on the CSI-RSsin the measurement set at step 602. Referring to FIGS. 3 and 4, the UE302 estimates the channels of the cells 300, 310, and 320 based on theCSI-RSs 401, 402, and 403 respectively in the measurement set of thecells having the resources allocated by the central controller. Assumingthat all cells in the measurement set are turned on, the UE calculatesSINRs for the respective cells to select the best cell. At this time,the UE calculates SINR for use in the DS mode and selects the best cellin consideration of additional cell conditions. Here, the blanking setfor the DB mode is determined by the central controller. Since theSINR-based cell selection method has been described with reference withFIG. 5, a detailed description thereof is omitted herein.

In the DB mode, one or more cells considered to produce potentialinterference to a certain cell mute data transmission for apredetermined time duration. Accordingly, the central controller has todetermine the cells to be off based on the feedback from the UE. It isnot necessary for the UE to acquire the information on the cells to beoff. In order to accomplish this, the central controller notifies the UEof at least one blanking set.

Assuming that the measurement set is {1, 2, 3, 4, 5, 6} and the UEreceives the blanking sets {1, 2} and {3, 4}, the UE is aware that thenumber of cells to perform measurement is 6 and the cells 1 and 2 or thecells 3 and 4 may turn off simultaneously. Here, the indices correspondto the respective CSI-RSs in the measurement set.

Under the assumption that the cells belonging to the blanking setnotified by the central controller have turned off, the UE calculatesSINR for the remaining cell. The UE selects the best cell in associationwith each blanking cell in consideration of an additional offset value.The UE can select the best cell in V′ blanking set as expressed byEquations (5) and (6).

i* _(k)=arg max_(i) └SINR(R _(i), Σ_(j∈M\{blanking) _(—) _(set) _(k,i})R _(j))+offset_(i) ^(SINR)┘  (5)

i* _(k)=arg max_(i) └SINR(R _(i), Σ_(j∈M\{blanking) _(—) _(set) _(k,i})R _(j))+ƒ(offset_(i) ^(MCS))┘  (6)

Once the best cell has been selected in each blanking set, the UE feedsback, to the central controller, the cell index of the best cell andchannel information in the state that all selected cells are turned onand the cell indices of the best cells in the respective blanking setsand the related channel information.

Returning to step 601, if it is determined that the UE is not a CoMP UE,the UE performs a non-CoMP operation at step 611. In the non-CoMPoperation, the UE performs channel estimation for the cell transmittingdata thereto and feeds back the channel status information to thecentral controller.

There are two feedback schemes for the UE to transmit the feedbackinformation for DB in the LTE-A system: periodic channel informationfeedback through Physical Uplink Control CHannel (PUCCH) andnon-periodic channel information feedback through Physical Uplink SharedCHannel (PUSCH).

The UE can perform the feedback in a predetermined order of the cells inthe state that all the cells are turned on through the PUCCH-basedperiodic channel information feedback. For example, it is possible toperform the first PUCCH feedback for the cells in the state that all ofthe cells are turned on, the second feedback for the first blanking set,and the third feedback for the second blanking set.

Once the PUCCH feedback has been completed for all blanking sets, thefeedback restarts in the state that all of the cells are turned on.

Like the PUCCH-based periodic channel information feedback, the UE canperform the feedback in a predetermined order of the cells in thePUCCH-based non-periodic channel information feedback, however, thepresent invention is not limited thereto. That is, the UE is capable ofdesignating a certain blanking set for feedback through the PDCCHincluding a field indicating activation of non-periodic feedback. Forexample, if the non-periodic feedback activation is indicated in thecontrol information transmitted through the PDCCH and if the secondblanking set feedback is indicated, the UE performs the non-periodicfeedback through the PUSCH. The feedback scheme indication can be madein such a way that feedback for more than one blanking set is indicatedthrough the PDCCH. In detail, a triggering bit may be introduced as anindicator triggering feedback of a specific interference status suchthat the feedback is triggered in response to the indicator.

FIG. 7 is a flowchart illustrating a feedback method in a DB-basedcellular mobile communication system adapted to the type of the UEaccording to an embodiment of the present invention. UEs can becategorized into three types: dynamic CoMP UE, semi-static CoMP UE, andnon-CoMP UE.

Referring to FIG. 7, the UE determines whether it is a dynamic CoMP UE.At this time, the CoMP UE can be determined based on the feedback moderequested by the central controller. That is, the central controllernotifies the UE of the feedback mode in which the UE is to operate, inadvance. The UE checks the feedback mode to determine whether it is aCoMP UE.

If it is determined at step 701 that the UE is a dynamic CoMP UE, the UEoperates in DB mode at step 702. In brief, the UE estimates the channelsof the respective cells based on the CSI-RSs in the measurement set. TheUE calculates SINRs of the respective cells, under the assumption thatall cells in the measurement set are turned on, to select the best cell.The UE also calculates, under the assumption that the cells belonging tothe blanking set in the measurement set are turned off, the SINR of theremaining cells to select the best cell. Next, the UE collects theinformation on the channels of the best cells in the measurement set andin the blanking set and sends the channel information to the centralcontroller.

If it is determined at step 701 that the UE is not a dynamic CoMP UE,the UE determines at step 711 whether it is a semi-static CoMP UE. Thiscan be determined based on the feedback mode requested by the centralcontroller. The semi-static CoMP UE is the UE receiving downlink datafrom a certain cell basically but, if the downlink transmission is mutedin the cell, receives the downlink data from another cell. Accordingly,it is not necessary for the semi-static CoMP UE to feed back to the eNBthe cell index of the best cell, but the channel information on the cellwhen blanking is not applied.

If it is determined at step 711 that the UE is a semi-static CoMP, theUE estimates the channel of the cell to be used without the existence ofany blanking set based on the CSI-RS supposed to be used when there isno blanking set at step 712. Next, the UE estimates the channel of thecell to be used with the existence of the blanking set based on theCSI-RS supposed to be used when there is the existence of any blankingset at step 713. Finally, the UE feeds back the channel informationobtained with and without existence of any blanking set to the centralcontroller.

If it is determined at step 711 that the UE is not a semi-static CoMP,the UE performs a non-CoMP operation at step 721. In the non-CoMPoperation, the UE performs channel estimation for the cell transmittingdata thereto and feeds back the channel information to the centralcontroller.

FIG. 8 is a schematic block diagram illustrating a UE according to anembodiment of the present invention.

As shown in FIG. 8, the UE includes a communication unit 810 and acontrol unit 820.

The communication unit 810 is responsible for radio communication fortransmitting/receiving data. Here, the communication unit 810 is capableof transmitting the channel information of the best cell under thecontrol of the control unit 820.

The control unit 820 controls configurations and operations of theinternal components of the UE. The control unit 820 selects the bestcell according to the communication states with the respective cells andfeeds back the channel information of the selected channel to thecentral controller. In order to accomplish this, the control unitincludes a channel estimator 830.

The channel estimator 830 determines, based on the feedback modenotified by the central controller, whether the UE is the CoMP UE andestimates the channel based on the CSI-RSs received according to thedetermination result. The channel estimator 830 controls thecommunication unit 810 to select the best cell based on the estimatedchannels and transmits the channel information on the best cell to thecentral controller.

In more detail, if the UE is the CoMP UE, the channel estimator 830estimates the channels of the respective cells based on the CSI-RSs inthe measurement set. Next, the channel estimator 830 calculates SINRs ofthe cells in the measurement set to select the best cell, under theassumption that all of the cells are turned on. The channel estimator830 also calculates, under the assumption that the cells of a certainblanking set in the measurement set are turned off, SINRs of theremaining cells to select the best cell in another blanking set. Thechannel estimator 830 feeds back the channel information about the bestcell in the all-cell-turned-on state and the best cells in the blankingsets to the central controller.

Although the description is directed to the case where the UE includesthe communication unit 810 and the control unit 820, the presentinvention is not limited thereto. That is, the UE may be provided withdiverse components according to the features of the UE. For example, theUE may include a display unit for displaying the operation state of theUE, an input unit for receiving user input for executing a specificfunction, and a storage unit for storing data generated in the UE.

FIG. 9 is a schematic block diagram illustrating a central controlleraccording to an embodiment of the present invention.

As shown in FIG. 9, the central controller includes a control unit 910and a communication unit 920.

The control unit 910 controls configurations and operations of theinternal components of the central controller. The control unit 910notifies the UE of a blanking set of cells that turn off to mute datatransmission at a predetermined time and cause potential interference toother cells in the DB mode. The control unit 910 allocates CSI-RSresources per cell for channel estimation of the CoMP UE and notifiesthe UE of the position of the resource. In order to accomplish this, thecontrol unit 910 includes a per-cell resource allocator 915.

The per-cell resource allocator 915 allocates CSI-RS resources in orderfor the UE receiving CoMP transmission to estimate the channels of therespective cells and transmit CSI-RSs on the corresponding resources.The resource is allocated for CSI-RS. A set of cells having at least oneCSI-RS for channel estimation of the CoMP UE is referred to asmeasurement set.

The communication unit 920 is responsible for data communication with aUE or a cell, which is controlled by the central controller. Thecommunication unit 920 transmits the CSI-RS on the allocated resourceand receives feedback of channel information from the UE under thecontrol of the control unit 910.

As described above, the feedback method and apparatus of the presentinvention is capable of performing CoMP transmission to the UE locatedat the cell edge in a cellular mobile communication system.

Also, the feedback method and apparatus of the present invention iscapable of providing improved mobile communication service through theCoMP transmission as compared to the non-CoMP transmission.

Also, the feedback method and apparatus of the present invention enablesa UE to select the cell for receiving data dynamically at the cell edge.

Also, the feedback method and apparatus of the present invention iscapable of turning off the cells causing potential interference in orderfor neighbor cells to cooperate for CoMP transmission to the UE locatedat the cell edge.

Furthermore, the feedback method and apparatus of the present inventionis capable of allocating high data rate to the UEs without regards totheir location within the cell, resulting in improved system throughput.

Although certain embodiments of the present invention have beendescribed in detail hereinabove with specific terminology, this is forthe purpose of describing particular embodiments only and not intendedto be limiting of the invention. While particular embodiments of thepresent invention have been illustrated and described, it would beobvious to those skilled in the art that various other changes andmodifications can be made without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. A method for transmitting channel information, bya User Equipment (UE), comprising: identifying information for at leastone first type Channel Status Information Reference Signal (CSI-RS) andinformation for at least one second type CSI-RS from an eNB; generatingfirst channel information based on a first set of a first type CSI-RSand a second type CSI-RS; generating second channel information based ona second set of a first type CSI-RS and a second type CSI-RS; reportingthe first channel information by Physical Uplink Control CHannel(PUCCH)-based periodic channel information feedback; and reporting thesecond channel information by the PUCCH-based periodic channelinformation feedback.
 2. The method of claim 1, wherein the second typeCSI-RS is zero power for interference measurement.
 3. The method ofclaim 1, wherein the first type CSI-RS is for channel measurement. 4.The method of claim 1, wherein the at least one first type CSI-RS istransmitted on allocated resources.
 5. The method of claim 1, whereinthe PUCCH-based periodic channel information feedback is predefined forthe first set of a first type CSI-RS and a second type CSI-RS, and forthe second set of a first type CSI-RS and a second type CSI-RSrespectively.
 6. A method for receiving channel information, by a eNB,comprising: transmitting information for at least one first type ChannelStatus Information Reference Signal (CSI-RS) and information for atleast one second type CSI-RS to a User Equipment (UE); receiving firstchannel information by Physical Uplink Control CHannel (PUCCH)-basedperiodic channel information feedback; and receiving second channelinformation by the PUCCH-based periodic channel information feedback,wherein the first channel information is generated based on a first setof a first type CSI-RS and a second type CSI-RS, and wherein the secondchannel information is generated based on a second set of a first typeCSI-RS and a second type CSI-RS.
 7. The method of claim 6, wherein thesecond type CSI-RS is zero power for interference measurement.
 8. Themethod of claim 6, wherein the first type CSI-RS is for channelmeasurement.
 9. The method of claim 6, wherein the at least one firsttype CSI-RS is received on allocated resources.
 10. The method of claim6, wherein the PUCCH-based periodic channel information feedback ispredefined for the first set of a first type CSI-RS and a second typeCSI-RS, and for the second set of a first type CSI-RS and a second typeCSI-RS respectively.
 11. A user equipment for transmitting channelinformation, comprising: a communication unit configured to transmit andreceive signals; and a control unit configured to control: identifyinginformation for at least one first type Channel Status InformationReference Signal (CSI-RS) and information for at least one second typeCSI-RS from an eNB; generating first channel information based on afirst set of a first type CSI-RS and a second type CSI-RS; generatingsecond channel information based on a second set of a first type CSI-RSand a second type CSI-RS; reporting the first channel information byPhysical Uplink Control CHannel (PUCCH)-based periodic channelinformation feedback; and reporting the second channel information bythe PUCCH-based periodic channel information feedback.
 12. The userequipment of claim 11, wherein the second type CSI-RS is zero power forinterference measurement.
 13. The user equipment of claim 11, whereinthe first type CSI-RS is for channel measurement.
 14. The user equipmentof claim 11, wherein the control unit is further configured to controltransmitting the at least one first type CSI-RS on allocated resources.15. The user equipment of claim 11, wherein the PUCCH-based periodicchannel information feedback is predefined for the first set of a firsttype CSI-RS and a second type CSI-RS, and for the second set of a firsttype CSI-RS and a second type CSI-RS respectively.
 16. An eNB forreceiving channel information, comprising: a communication unitconfigured to transmit and receive signals; and a control unitconfigured to control: transmitting information for at least one firsttype Channel Status Information Reference Signal (CSI-RS) andinformation for at least one second type CSI-RS to a User Equipment(UE); receiving first channel information by Physical Uplink ControlCHannel (PUCCH)-based periodic channel information feedback; andreceiving second channel information by the PUCCH-based periodic channelinformation feedback, wherein the first channel information is generatedbased on a first set of a first type CSI-RS and a second type CSI-RS,and wherein the second channel information is generated based on asecond set of a first type CSI-RS and a second type CSI-RS.
 17. The eNBof claim 16, wherein the second type CSI-RS is zero power forinterference measurement.
 18. The eNB of claim 16, wherein the firsttype CSI-RS is for channel measurement.
 19. The eNB of claim 16, whereinthe communication unit is configured to receive the at least one firsttype CSI-RS on allocated resources.
 20. The eNB of claim 16, wherein thePUCCH-based periodic channel information feedback is predefined for thefirst set of a first type CSI-RS and a second type CSI-RS, and for thesecond set of a first type CSI-RS and a second type CSI-RS respectively.